The present invention is directed generally to an improved gas return railway car hydraulic cushioning device and more particularly to such a device including a simple rugged end cap which includes an interiorly directed protrusion for cooperating with one or more ball valves near the adjacent end of the high pressure cylinder to accomplish valving of hydraulic fluid from the main reservoir into the interior of the high pressure cylinder in response to relative movement between the piston and cylinder in one direction.
The cushioned under frame of a railway car generally includes a pair of end-of-car cushioning devices or gears at opposite ends of the car for providing a resilient or hydraulically controlled connection between the center sill and coupler. Each gear includes a hydraulic system consisting of two chambers related by valves and ports. These include the high pressure inner cylinder having a piston reciprocally moveable therein and the low pressure outer housing.
Impact energy from coupling, starting and stopping forces is transmitted from the coupler through the outer housing and hydraulic cylinder system to the center sill of the railway car. As the cylinder closes on the piston through impact, oil is forced from the cylinder into the outer housing through metering ports appropriately sized and placed. The oil is instantly returned behind the piston so that hydraulic cushioning is continuously provided within the cylinder when both draft and buff forces are exerted on the railway car.
When external forces are removed from the hydraulic cushioning device, the piston should be returned to a neutral position so that the device can effectively cushion the next impact. Restoring forces have conventionally been provided either by the repositioning springs of a separate restoring mechanism or by pressurized gas within the cushioning unit itself. Spring restoring mechanisms generally have the disadvantage of directing the restoring force along a line offset below the center line of the main cylinder, thereby inducing a canting of the cushioning device within the sill. Whereas gas return hydraulic cushioning units eliminate the off center forces and maintenance problems associated with mechanical restoring mechanisms, most are either expensive to manufacture, or they produce an unpredictable spongy cushioning action. An improved gas return hydraulic cushioning unit is disclosed in Conley et al., U.S. Pat. No. 4,805,517, wherein the mixing of gas and hydraulic oil in the chambers interiorly and exteriorly of the high pressure cylinder unit is avoided by strategic placement of metering ports through the cylinder wall at positions below the level of gas in the exterior chamber. Whereas that invention is believed to have provided a substantial advance in the art, it nevertheless included the conventional and complicated internal valving plate assembly at the rod end of the high pressure cylinder for return flow of hydraulic oil into the main cylinder behind the piston in response to buff forces on the railway car. That valving plate included numerous parts including the plate subject to bending, valves which can lock up, springs which could lose tension, and seals which wear out, adding to both the expense and required maintenance for the hydraulic cushioning unit.
Accordingly, a primary object of the invention is to provide an improved hydraulic cushioning unit.
More specifically, an object of the invention is to provide an improved gas return hydraulic cushioning unit including a simple rugged end cap adapted to cooperate with ball valves in the adjacent end of the high pressure cylinder to accomplish valving of hydraulic fluid from the main reservoir into the high pressure cylinder.
Another object is to provide such a unit of simple and economical construction.
Another object is to provide such a unit with minimum maintenance requirements.
Another object is to provide such a unit which affords internal mechanical cushioning of the piston in the limit position thereof in response to draft forces on the railway car.
Another object is to provide such a unit with a simple rugged end cap which closes one end of the cylinder and housing, affords mechanical cushioning for the piston and cooperates with ball valves in the adjacent end of the high pressure cylinder to afford valving of hydraulic fluid flow from the main reservoir to the high pressure cylinder.
Finally, another object is to provide a gas return railway car hydraulic cushioning unit which is simple and rugged in construction, economical to manufacture and efficient in operation.